Multiple setup-and-loop blocks possible using the backpack.

[BjoernLuig]

Describe the bug
Multiple setup-and-loop blocks are possible using the backpack.

To Reproduce
Steps to reproduce the behavior:

1. Put setup-and-loop block in the backpack.
2. Pull setup-and-loop block out of the backpack.
   -> Second setup-and-loop block is now present and not removable.

Expected behavior
It should at least be possible to remove a second setup-and-loop block if not needed. At best, it shouldn't be possible to create a second one.

Screenshots